Inhibition of cyclic AMP response element-binding protein cyclic AMP response element-mediated transcription by the immunosuppressive drugs cyclosporin A and FK506 depends on the promoter context

The immunosuppressants cyclosporin A and FK506 (tacrolimus) can block the p hosphatase calcineurin, thereby inhibiting gene transcription directed by t he cyclic AMP (cAMP)- and calcium-responsive transcription factor, cAMP res ponse element (CRE)-binding protein, and its binding site, CRE, in various cell lines. This action is a novel molecular mechanism of cyclosporin A and FK506 action. Because inhibition of CREB/ CRE-directed transcription by cy closporin A and FK506 has previously been observed by using synthetic minie nhancers reporter fusion genes were constructed to ex-amine the effect of c yclosporin A and FK506 on the transcriptional activity of CRE-containing na tural promoters. In transient transfection experiments, cyclosporin A and F K506 inhibited the transcriptional activation by cAMP and the membrane depo larization of three CRE-containing promoters. However, cyclosporin A and FK 506 failed to inhibit the activation by cAMP of another promoter, the rat i nsulin I gene promoter. The lack of cyclosporin A/FK506 sensitivity is not intrinsic to the insulin CRE because cyclosporin A and FK506 inhibited the activation by cAMP of the insulin CRE when isolated and used as a synthetic minienhancer. Rather, cyclosporin A/FK506 resistance may be conferred by s pecific promoter interactions because a mutational analysis of the insulin promoter revealed that inside this promoter, CRE activity depends on an adj acent control element. These data show that cyclosporin A and FK506 can inh ibit CRE activity when the CRE resides in its natural promoter. However, th e cyclosporin A/FK506 sensitivity depends on the specific promoter context. The results suggest that cyclosporin A and FK506 may alter target tissue f unction through the regulation of a subset of CRE-containing genes.